Fixed create label form not working on issue boards in a sub-group project

Closes #31862

app/views/projects/boards/components/sidebar/_labels.html.haml

@@ -19,7 +19,7 @@
         ":value" => "label.id" }
       .dropdown
         %button.dropdown-menu-toggle.js-label-select.js-multiselect.js-issue-board-sidebar{ type: "button",
-          data: { toggle: "dropdown", field_name: "issue[label_names][]", show_no: "true", show_any: "true", project_id: @project.id, labels: namespace_project_labels_path(@project.namespace, @project, :json), namespace_path: @project.try(:namespace).try(:path), project_path: @project.try(:path) },
+          data: { toggle: "dropdown", field_name: "issue[label_names][]", show_no: "true", show_any: "true", project_id: @project.id, labels: namespace_project_labels_path(@project.namespace, @project, :json), namespace_path: @project.try(:namespace).try(:full_path), project_path: @project.try(:path) },
           ":data-issue-update" => "'#{namespace_project_issues_path(@project.namespace, @project)}/' + issue.id + '.json'" }
           %span.dropdown-toggle-text
             Label

changelogs/unreleased/issue-boards-sidebar-create-new-label-404-error.yml

+---
+title: Fixed create new label form in issue boards sidebar
+merge_request:
+author:

spec/features/boards/sub_group_project_spec.rb

+require 'rails_helper'
+
+describe 'Sub-group project issue boards', :feature, :js do
+  include WaitForVueResource
+
+  let(:group) { create(:group) }
+  let(:nested_group_1) { create(:group, parent: group) }
+  let(:project) { create(:empty_project, group: nested_group_1) }
+  let(:board) { create(:board, project: project) }
+  let(:label) { create(:label, project: project) }
+  let(:user) { create(:user) }
+  let!(:list1) { create(:list, board: board, label: label, position: 0) }
+  let!(:issue) { create(:labeled_issue, project: project, labels: [label]) }
+
+  before do
+    project.add_master(user)
+
+    login_as(user)
+
+    visit namespace_project_board_path(project.namespace, project, board)
+    wait_for_vue_resource
+  end
+
+  it 'creates new label from sidebar' do
+    find('.card').click
+
+    page.within '.labels' do
+      click_link 'Edit'
+      click_link 'Create new label'
+    end
+
+    page.within '.dropdown-new-label' do
+      fill_in 'new_label_name', with: 'test label'
+      first('.suggest-colors-dropdown a').click
+
+      click_button 'Create'
+
+      wait_for_ajax
+    end
+
+    page.within '.labels' do
+      expect(page).to have_link 'test label'
+    end
+  end
+end